amplify-js: TypeError on API request.

** Which Category is your question related to? ** API ** What AWS Services are you utilizing? ** API Gateway ** Provide additional details e.g. code snippets ** I’m trying to add a REST API as this example:

https://aws-amplify.github.io/docs/js/api#post

The headers I set like the following:

let myInit = {
    body: {},
    headers: {
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Credentials": true
    }
  };

But there is an error

error TypeError: headers[key].trim is not a function
    at Signer.ts:110
    at Array.map (<anonymous>)
    at canonical_headers (Signer.ts:105)
    at canonical_request (Signer.ts:155)
    at Function.Signer.sign (Signer.ts:314)
    at RestClient._signed (RestClient.ts:279)
    at RestClient.ts:148

I’m using Amplify in React aws-amplify@2.2.1 aws-amplify-react@3.1.2

Thanks for any help!